A curette is a surgical instrument with a handle, a shaft, and a cup- or spoon-shaped tip. The curette is used for scraping and scooping out bone spurs and other diseased or injured bodily tissues. In one particular application curettes are used in spinal surgery for the removal of bone spurs from vertebrae. The edge of the cup-like tip has a sharpened rim to enhance its effectiveness for scraping and cutting bone.
In use, the tip of the curette is placed into the area of tissue to be removed and scraped against the tissue. When the cup is filled the instrument is removed from the wound and the tissue within the cup is emptied. This process constitutes a "pass." The instrument is then returned to the wound, where the process is repeated until all the diseased or damaged tissue has been removed. When using conventional curettes for micro-spinal surgery, 12 to 14 passes are usually required to remove a bone spur.
A number of curettes are known in the art. One such curette is the flat-edged curette. The tip of this curette is positioned on a shaft, the longitudinal axis of which is parallel to and collinear with the longitudinal axis of a round handle. For the removal of cancellous bone with a flat-edged curette axial rotation of the curette is not sufficient. To be effective the tip must pivot around the longitudinal axis. Thus, this design is not suitable for curettage of bone or ligament in a limited space such as the spinal canal.
Another curette is the angle-edged curette. The angle-edged curette has a tip which is angled at 15.degree. to the longitudinal axis. The longitudinal axis of the shaft is also parallel to and collinear with the longitudinal axis of the handle. The angle-edged curette is an improvement on the flat-edged design in that it does not have to be pivoted around the longitudinal axis to be effective. Rotation of the angle-edged curette around the longitudinal axis automatically provides the circular movement of the tip with a greater radius, resulting in a significantly improved performance of bone curettage and cancellous bone removal. However, in use the fingers of the user, grasping the handle, often obscure the view of the tip, making delicate procedures difficult and potentially dangerous.
Another design is that described in U.S. Pat. No. Des. 312,310. In this curette design the shaft is neither collinear nor parallel with the handle, but instead is placed on one side of a square cross-sectional handle. The shaft is angled toward the axis of the handle which places the tip in a position which is collinear with the axis of the handle. However, in this design the user's fingers also obscure the view of the tip in the field of the microscope used for the microsurgery. Accurate placement of the tip is difficult when the view of the tip of the curette is obscured by the fingers of the user during use. Moreover, the square cross-sectional handle makes rotation of the curette difficult. Another feature of this design is that the tip of the curette is angled. While this angle makes scraping of tissue easier, the tip is susceptible to breakage allowing this small piece of the curette to drop into the site of the surgery. The tip must be recovered before completion of the surgical procedure and "hunting" for the broken tip increases the possibility of unintentional damage to tissue at the site of the surgery.
Another curette design is a ring curette. This type of curette is one in which the cup of the tip does not have a bottom and the tip is in the form of a ring. This type of curette is used for soft tissue removal and is not suitable for the removal of bone.
There is a need for a curette for use in micro-spinal surgery which allows the user to place the device to accurately and to "set" the edge of the curette to effectively remove the desired tissue. It is also desirable that the tip of the curette is sufficiently strong to withstand the forces placed on it during normal use without breaking. It is also desirable that only are a few passes are required to remove bone spurs.